I am not an expert in AppImage but I think the main thing is it is pretty easy to make a XAR of a Python script and that the overhead is probably less (especially for repeated invocations).
I think XAR is simpler than the other alternatives; they have more complex specifications, being aimed at distributing full GUI applications (though I bet they work fine for these kinds of use cases, modulo perhaps quick and easy conversion of a Python program into a XAR). I suspect, but haven't measured, that XAR has lower execution overhead since it will re-use a mount point if a tool is recently invoked, rather than remounting every time.
One thing XAR doesn't really try to do is work cross-platform. It will rely on the system Python, for instance, rather than embed the interpreter and all libraries inside (it will embed the libraries your tool depends on that aren't part of Python itself). This is a pro in some cases (lower overhead), but a con if you want something you can carry across wildly different systems.
I think XAR is simpler than the other alternatives; they have more complex specifications, being aimed at distributing full GUI applications (though I bet they work fine for these kinds of use cases, modulo perhaps quick and easy conversion of a Python program into a XAR). I suspect, but haven't measured, that XAR has lower execution overhead since it will re-use a mount point if a tool is recently invoked, rather than remounting every time.
One thing XAR doesn't really try to do is work cross-platform. It will rely on the system Python, for instance, rather than embed the interpreter and all libraries inside (it will embed the libraries your tool depends on that aren't part of Python itself). This is a pro in some cases (lower overhead), but a con if you want something you can carry across wildly different systems.